The present disclosure relates to knock sensors, in particular engine knock sensors.
Most vehicles today are equipped with numerous sensors that are used to regulate the operation of the engine. One such sensor is an engine knock sensor. Typically, an engine knock sensor is mounted on an engine block, e.g., on the intake manifold or a cylinder head. The knock sensor is adapted to produce an output voltage in proportion to engine vibrations caused by uneven burning of fuel (e.g., engine knock). When engine knock occurs, a microprocessor adapted to receive signals from the knock sensor is also adapted to adjust the engine timing in order to minimize or eliminate the sensed knocking.
Current knock sensors include a piezoelectric element that is preloaded such that the sensor will provide an output voltage in proportion to engine vibrations caused by knock. Typically, the resonant frequency of the sensor is matched to the knock frequency of the engine. If the sensor determines there is an engine knock, a corresponding signal is generated, which is received by the engine control module (ECM) to control the knock by for example, retarding the spark timing of the engine.
A knock sensor 10 of a known construction is illustrated in FIG. 1. Knock sensor 10, comprises a sleeve portion 12, which includes a disc shaped flange portion 14 and a cylinder portion 16 that extends from a center portion of the flange portion. An external thread portion 18 is formed at an upper portion of the cylinder portion.
An assembly of a piezoelectric element 20 disposed between a first contact plate 22 and a second contact plate 24 is positioned on sleeve 12 by being slid over cylinder portion 16. The contacts are insulated to ensure proper operation of the sensor. The insulation is provided by a first layer of insulation 26 and a second layer of insulation 28, which may be positioned in any configuration to ensure insulation of the contact plates and piezoelectric element assembly as well as ensure electrical communication with terminal portions of contact plates 22 and 24, wherein a signal indicative of knock may be generated by the knock sensor. For example, the insulating layers may be disposed between the contact plate and the flange portion or the contact plates and the cylinder portion or combinations thereof. Also, a layer of insulation is provided between the upper contact plate 24 and a seismic mass 30, which is positioned over cylinder portion 16 and adds the required mass to the sensor.
In order to secure the assembly together and provide the necessary pre-load to the piezoelectric element 20 a nut 32 configured to threadingly engage the threaded portion 18 of the cylinder is secured to the cylinder until the nut applies the required pre-load to the piezoelectric element through a spring 34 disposed between the mass and the nut. Once assembled the outer periphery of the sensor is encased in a housing or covering 36, which is configured to encase the sensor in a manner that allows a bolt to pass through the center of the sleeve for securing the same to the engine block. The housing also provides a means for termination of the leads of the two contact plates.
Accordingly, the assembly of the knock sensor described above includes multiple parts and multiple assembly steps. Moreover, the additional parts add to the overall size of the completed sensor. For example, in one assembly process, the first insulating layer 26 is disposed on the sleeve, then the lower contact plate 22, the piezoelectric element 20 and the upper contact plate 24 are disposed on the first insulating layer and the second insulating layer 28 is disposed on the upper contact plate 24, then the mass 30 and spring 34 via application of nut 32 to the sleeve preloads the piezoelectric element 20. Finally, the assembled elements are covered with the cover portion 36. The resulting size of the completed sensor is directly proportional to the number and configuration of the components encased by the housing. In addition, the number of assembly steps is also directly proportional to the number of parts assembled on the sleeve 12.
Accordingly, there is a continuing need to reduce the size of the knock sensor while achieving the same output of a larger sensor.
A knock sensor having a piezoelectric transducer pre-loaded by a seismic mass, wherein the seismic mass is configured to threadingly engage a portion of a sleeve of the sensor in order to pre-load the piezoelectric transducer.
A knock sensor, comprising: a sleeve; a piezoelectric transducer disposed about the sleeve, the piezoelectric transducer being insulated from the sleeve and in electrical communication with a first terminal and a second terminal; wherein the piezoelectric transducer is preloaded by a combination seismic mass and nut configured to threadingly engage a portion of the sleeve and provide a mass to the knock sensor, the combination seismic mass and nut being integrally formed out of the same material.
A knock sensor adapted to provide a signal to an engine control module of an engine, the signal corresponding to a knock vibration of the engine, the knock comprising: a sleeve; a piezoelectric transducer disposed about the sleeve, the piezoelectric transducer being insulated from the sleeve and in electrical communication with a first terminal and a second terminal; wherein the piezoelectric transducer is preloaded by a combination seismic mass and nut configured to threadingly engage a portion of the sleeve and provide a mass to the knock sensor, the combination seismic mass and nut being integrally formed out of the same material and either the first terminal and/or the second terminal are in electrical communication with the engine control module.